This invention relates to apparatus for dispensing semi-fluid materials such as cream fillings for bakery products. In machinery for mass producing bakery products raw materials for such fillings are mixed and supplied in a semi-fluid state under pressure to a dispensing apparatus. Such dispensing apparatus includes a frame which supports a conveyor and a movable dispensing head. The dispensing head customarily includes a manifold which receives the semi-fluid mixture under pressure from the mixer, a nozzle plate, a slider valve between the manifold and nozzle plate and a needle plate having a number of dispensing needles connected thereto.
The nozzle plate includes a number of vertical bores each of which extends between the slider valve and one or more channels opening into the needle plate. A transverse bore having a movable piston mounted therein connects with each of the vertical bores and provides suction pressure to draw the semi-fluid material to be dispensed back into the nozzle plate in a manner described more fully below. The nozzle plate includes a number of channels connecting through apertures in the needle plate to the input openings of a number of needle-like dispensing members which extend downwardly from the needle plate and terminate in dispensing orifices.
Sheets or pans containing the products to be filled are moved under the dispensing head by the conveyor of the dispensing apparatus. The dispensing head is then lowered causing the needle-like members to pierce the products. When the slider valve is opened and the movable piston is activated, the semi-fluid material is forced under pressure through the nozzle plate and through the needle plate into the needle-like dispensers. The material passes through the apertures in the needle-like dispensers and into the products to be filled. After one group of products has been filled the slider valve is closed, the piston is returned to its original position and the dispensing head is lifted in preparation for filling the next group of products which the conveyor moves into filling position.
Because the semi-fluid material must pass through relatively narrow passages and because it is customarily aerated, there is a tendency for it to continue to expand after the slider valve has closed causing it to extrude from the apertures in the needle-like dispensers during and after their withdrawal from the products to be filled. This is undesirable since this excess of extruded semi-fluid material will be dripped or smeared onto the exterior surface of the next group of products to be filled resulting in unsightly products.
The piston mentioned above is intended to prevent the extrusion of this excess semi-fluid material by creating a suction in the system when it returns to its original position. Since the slider valve is closed when the piston returns this suction is applied through the needle plate to the dispensing needles and sucks this material back into the needles. In prior art apparatus of this type a spring has been utilized to return the piston to its starting position and thereby create the desired suction pressure. It has been found, however, that the spring used for this purpose is prone to frequent failures with the result that the piston returns too slowly or completely fails to return and the necessary suction pressure is not provided. The present invention solves this prior art problem by providing an improved more reliable means to return the piston to its starting position within the transverse bore.
It is also important that the fluid pressure at the output of each of the needle-like dispensers be equal in order to insure uniform filling of each product. Since customarily several of these needle-like dispensers are supplied from a single inlet port through channels formed in the lower surface of the nozzle plate which channels communicate with apertures extending through the needle plate to individual dispensing needles located at varying distances from this inlet port it has been difficult to insure that a uniform amount of the semi-fluid material will be dispensed by each needle. In the past it has been customary to provide a larger or smaller needle plate apertures depending upon the distance of the applicable needle from the input aperture in an effort to equalize the fluid pressure at the input of each dispensing needle. This solution required the use of very small diameter apertures to service those needles closest to the input aperture. These very small apertures tended to become clogged. The present invention solves this problem by configuring the channels in the lower surface of the nozzle plate to provide a uniform pressure drop between the inlet port and each of the needle-like dispensers.